The present invention relates to a signal demodulating apparatus.
As a signal demodulating apparatus related to the present invention, a PAL (phase alternation line) signal demodulating apparatus will be described hereinbelow by way of example, with reference to FIG. 4. In the PAL signal demodulating apparatus shown in FIG. 4, capacitors C1 and C2, a resistor R1, a variable resistor R3, a tank coil L1 and a coil L2 are provided as external parts at the periphery of a delay line 12 (e.g., a glass delay line). The capacitor C2 and the variable resistor R3 are connected in series between an input terminal 32 ( to which a PAL chroma signal is inputted) and a node N3. The node N3 is directly connected to one input terminal of the delay line 13 and to the other input terminal thereof via the coil L2.
With respect to two output terminals of the delay line 12, on the other hand, a node N1 is connected to one output terminal and a node N2 is connected to the other output terminal thereof. Further, the node N1 is grounded via the capacitor C1. The tank coil L1 and the resistor R1 are connected in parallel to each other between the nodes N1 and N2. The node N2 is connected to an output terminal 31. In the above-mentioned signal demodulating apparatus, a PAL chroma signal inputted through the input terminal 32 is outputted from the output terminal 31 as a delay signal after having been delayed by about 64 .mu.sec (which corresponds to one horizontal line ).
In the above-mentioned signal demodulating apparatus, the delay time of the delay line 12 inevitably disperses due to manufacturing error. The dispersion of the delay time has been so far regulated manually product by product by adjusting the values of the externally connected parts, for instance by changing the resistance value of the variable resistor R3 and the inductance L of the tank coil L1, thus causing an increase in the manufacturing cost thereof. In addition, although the delay time changes with the lapse of time, the abovementioned signal demodulating apparatus cannot cope with a change caused by the aged deterioration.